It is expected that the oxygenation status of tissues may be a significant factor in the progression of the healing of wounds. Wound healing is profoundly influenced by local blood supply, vasoconstriction, and all other factors that govern perfusion and blood oxygenation. It is generally believed that impaired perfusion and oxygenation are the most frequent causes of healing failure, and wounds in highly vascularized tissues (e.g., head, anus) heal fast and are quite resistant to infection. The availability of such data, combined with a means to measure the pO2 in healing wounds, would provide a powerful tool to improve clinical treatment of wounds. The group at Northwestern has developed several well characterized models for making wounds and following their healing. The purpose of this collaborative study is to explore the possibility of using EPR oximetry to investigate the role of actual pO2 on critical parameters relevant to wound healing - specifically, to measure the tissue pO2 at different stages of the wound healing process, and at different locations in and around the wound. Studies have been initiated in which paramagnetic particulate materials are inserted into the regions of the wounds and equivalent areas in which no wound is made. The effect of ischemia and aging on pO2 of wounded tissue also is being studied. Using gloxy as the oxygen-sensitive material, we have carried out initial studies with two wound healing models: mouse ischemic flap model, and ischemia rat ear model. By implanting gloxy particles (about 0.5-0.8 mm in diameter) in three different sites in the wounded area of a rat ear, as well as in the opposite control ear, we were able to measure tissue pO2 at different sites by placing the resonator over the region of interest.